Saturday, February 6, 2016

Radon: Scourge or Blessing for Mankind?

Government was tightening industrial radioactive emission standards to ridiculously low levels, while demanding that homeowners modify their homes to the point where radon doses to the average citizen were hundreds of times greater than the levels dictated to nuclear workers.

Radon is the heaviest of the "noble gases," so named because it - like its cousins neon, argon, krypton, and xenon - does not react with other elements to form compounds. It is radon's "nobility" that minimizes its effects on the body, since it is mostly a transient that is breathed in and then expelled without any chemical reaction taking place. When radon decays in the body, however, it spawns a series of short half-life progeny that are not only chemically reactive with tissue, but are - as we would suspect from their half-lives - also highly radioactive.

[When uranium decays (which isn't very often with a half-life of 4.5 billion years), the products of the decay go through four more stages (taking a couple of million years) until radium is formed. With a half-life of 1,600 years, radium 226 decays into radon gas with a half-life of 3.8 days. The daughters of radon are polonium 218, lead 214, bismuth 214, polonium 214 - and a couple of others. The aforementioned have very short half-lives and are therefore highly radioactive.]

Hazard to Miners?

For years, radon has been thought to be a hazard to miners, and a special confusing unit of activity - the Working Level (WL) - was derived to measure the danger. [One WL is the activity of air containing 100 pCi (3.7 Bq) of radon in equilibrium with its daughters (which, by the way, virtually never happens in the real world) per liter of air. For an approximation, a Working Level Month (WLM) is equivalent to a one-time whole body dose of about 300 mrem (0.3 cGy).]

Recently, however, as evidence of radiation hormesis has emerged, the jury is back out to deliberate a reconsideration of radon's guilt. It is now recognized that other carcinogens - in particular, the particulates suspended in the air of all mines and, more recently, the fumes from diesel engines - were present, but never considered. Radon was assumed to be the carcinogenic culprit, a theory that appears now to be based on flimsy circumstantial and anecdotal evidence.

A related re-evaluation of lung cancer in the Joachimsthal mining community [a famous mine in Czechoslovakia] noted that victims were invariably "pensioners," i.e. miners (not their unexposed, above-ground cohorts) who had made it to a retirement age, which was about ten years longer than their life expectancy. One might easily speculate that the cancer was caused by microscopic dust lodged in the lungs, and the miners' long lives a beneficial product of radon gas. [One of Europe's most famous health spas is Bad Gastein near Salzburg, Austria, which advertises "air with the highest radon content in Europe." The activity of its water is noted in Table 6, in this blog's entry on Monday, January 25, "Specific Activities."]

There has also been a piece of the puzzle right under our noses.

Radon gives its dose of mixed radiation primarily to the bronchial epithelium (fancy scientific words for "windpipe"), hence one would expect cancers caused by radon to be concentrated in this area. Au contraire! The miners' cancers are deep in the lungs [Nobel Laureate Rosalyn Yalow, Radiation and Society, Interdisciplinary Science Reviews, 16, 4, 1991], similar to the cancers caused by the South African amphibole-type asbestos [not to be confused with the common, domestic serpentine type of asbestos, which has not been shown to cause disease], used in ships because of its resistance to brine, acids, and oils.

It is difficult not to see the parallel between non-degradable asbestos fibers in the lungs and non-soluble silica particulates found in most mining environments.